1. Field of the Invention
The present invention relates generally to the field of petroleum coking processes. More specifically, the present invention relates to modifications of petroleum coking processes for the production of a form of petroleum coke that has characteristics that will allow it to be used as a diesel engine fuel. This invention also relates generally to the use of this new formulation of petroleum coke for the production of energy in diesel engine generation systems that typically use liquid or gaseous hydrocarbon fuels.
2. Description of the Related Art
Petroleum coke is a carbonaceous solid produced by the coker unit in crude oil refineries after crude oil has been subjected to a fractional distillation process. As shown in Prior Art FIG. 1, crude oil is separated into fractions through fractional distillation, in which petroleum fractions with lower boiling points, such as kerosene and diesel oil, are separated out from heavier fractions, such as asphalt and petroleum coke. Heavier sour crude oil supplies now entering the market are increasing the amount of heavy residuals available for processing into petroleum coke.
Thermal cracking processes were developed to convert as much of the heavy crude oil fractions into lighter products as possible. These refinery processes evolved into the modern coking processes that are currently used to upgrade the heavy residuals remaining after removing the lighter products from the crude oil refinery feedstock.
Modern coking processes employ thermal decomposition (or “cracking”) to maximize the conversion of low-value heavy residuals to lower boiling point hydrocarbon products. Coker feedstocks typically consist of non-volatile, asphaltic and aromatic materials with “theoretical” boiling points exceeding 1000° F. at atmospheric pressure. The boiling points are “theoretical” because these materials coke or crack from thermal decomposition before they reach such temperatures.
Coking feedstocks of heavy residuals normally consist of refinery process streams which cannot economically be further distilled, catalytically cracked, or otherwise processed to make fuel-grade blend streams. Typically, these materials are not suitable for catalytic operations because of catalyst fouling and/or deactivation by ash and metals. Common coking feedstocks include atmospheric distillation residuum vacuum distillation residuum, catalytic cracker residual oils, hydrocracker residual oils, and residual oils from other refinery units.
Consequently, coking feedstocks vary substantially among refineries. Their composition and quantity primarily depend on (1) the crude oil feedstock, (2) refinery processing equipment, and (3) the optimized operation plan for any particular refinery. In addition, contaminant compounds, which occur naturally in the crude oil, generally have relatively high boiling points and relatively complex molecular structures. Many of the materials or byproducts in the refinery become coke feedstock, and their contaminants usually end up in the petroleum coke by-product.
There are three major types of modern coking processes currently used in refineries to convert the heavy crude oil fractions into lighter hydrocarbons and petroleum coke: Delayed Coking, Fluid Coking, and Flexicoking. In all three of these coking processes, the petroleum coke is considered a by-product that is tolerated in the interest of more complete conversion of refinery residues to lighter hydrocarbon compounds. These lighter hydrocarbon compounds range from pentanes to complex hydrocarbons with boiling ranges typically between 350 and 950° F. The heavier cracked liquids (e.g. gas oils) are commonly used as feedstocks for further refinery processing that transforms them into transportation fuel blend stocks. A petroleum coke known as shot coke can also be created in the coking process described above.
Coking processes have been improved over time with improvements related to increasing the yield and recovery of cracked liquids and decreasing the coke yield. The content of volatile material in the resulting petroleum coke has been continually decreased, where possible. Various patents disclose improvements to the delayed coking process that include, but are not limited to, (1) coker designs that reduce drum pressures, (2) coker designs to provide virtually no recycle, and (3) periodic onstream spalling of heaters to increase firing capabilities and run length at higher heater outlet temperatures. These technology advances have been implemented in an effort to maximize the cracked liquid yields of the delayed coke and reduce petroleum coke yields and volatile content.
Other modifications of these coking processes introduce various wastes for disposal. Several patents disclose various means to inject certain types of oily sludges. Other prior art uses these coking processes for the disposal of used lubricating oils. Additional patents disclose the use of these coking processes for the disposal of other wastes. In general, these patents discuss the potential limited impact on the coke yield and volatile content, and promote other means to negate any increases. Also, these waste disposal techniques often increase the ash content of the coke and can introduce additional, undesirable impurities, such as sodium. Consequently, the objectives of these patents are to reuse or dispose of these wastes rather than enhance the petroleum coke properties.
U.S. Pat. No. 6,168,709 teaches the process to reduce specific contaminants in the petroleum coke order to increase the volatile composition of the pet coke for use in boiler systems and other systems discussed specifically as a replacement fuel for solid fuels such as coal.
U.S. Pat. No. 4,481,101 describes a method for further refining coker feedstock to remove metals and other contaminants from petroleum coke.
Various combustion technologies have been developed to overcome the combustion issues in petroleum coke. Specially designed combustion systems (noted above) include fluidized bed combustion, pyrolysis/gasification systems, and low heat capacity furnaces (i.e. without heat absorption surfaces). In general, these systems are cumbersome, expensive, and can require very large obtrusive structures. Several patents also disclose technologies to grind and stabilize coke/oil mixtures for use in conventional combustion systems. However, the quality of the traditional petroleum coke used in these fuel mixtures normally limits (1) the particle size distribution of the solids and (2) the degree of combustion (i.e. carbon burnout). The prior art has not addressed the specific combustion issues associated with producing petroleum coke with specific requirements for use in diesel engine systems.
Diesel engine systems have requirements for low levels of contaminants that form abrasive ashes such as aluminum and silicon to the degree that the combination of such metals are not greater then 80 ppm by weight in the liquid fuel prior to centrifugal separators reducing these impurities to an acceptable level. Petroleum cokes have impurities including sulfur and heavy metals (silicon, aluminum, vanadium, etc.).